Heart rate reduction

[bob392]

I have a friend who is 60 years of a age and about 100lbs overweight.  She went to the cardiologist because of lack of energy and shortness of breath. He put her on the treadmill and her heart rate actually decreased. He seemed concerned and is sending her to another cardiologist. What could be the possible reasons for the decrease in heart rate with exercise? Is this a sign of heart disease?

[kenkeith]

The brady-cardiac response to exercise can be due to increased stroke volume and also reflective of improved exercise economy, but that can be ruled out as the post suggests physical fitness is not a consideration.

The mechanism regulating exercise induced bradycardia is not thoroughly understood, but may be related to a change in the balance between the sympathetic and parasympathetic activity. In other words there is a disconnect during exercise between the craniosacral portion of the automatic nervous and central nervous system that decreases the rate of firing of the SA node (origin of the electrical impulse).

As we know the heart is programmed to increase its contractions when the system demands more oxygen, and apparently there is an interuption and modification of the program.  There are drugs (medication, ie ivabradine, atenolol) that can influence the heart rate during exercise.